The present invention relates to an exposure method for transferring a pattern image on a mask substrate onto a target exposure substrate by scanning the mask substrate and the target exposure substrate in synchronism, and a scanning exposure apparatus employing this method. Such an exposure apparatus is used in the manufacture of devices, e.g., a semiconductor chip such as an IC or LSI, a liquid crystal panel, a CCD, a thin-film magnetic head, a micromachine, or the like.
Among semiconductor exposure apparatuses, a step-by-step movable exposure apparatus (a so-called stepper), in which a stage mounted with a wafer is positioned within a plane and exposure is repeated, has been mainstream. In recent years, an increase in micropatterning degree of semiconductor circuits allows the advent of a so-called scanning exposure apparatus in which a mask substrate (reticle), where a circuit pattern is drawn, and a target exposure substrate (wafer) are mounted on stages, respectively, and are exposed while being scanned in synchronism. An expectation for this scanning exposure apparatus has been increasing. This is partly because a larger exposure field can be obtained than in a stepper so that the contrast can be set uniform easily, which is a feature unique to scanning exposure.
Although the scanning exposure apparatus has the advantage as described above, it has a disadvantage in that, when compared to the stepper, the time required for exposing one wafer entirely is difficult to shorten, i.e., the throughput of the apparatus is difficult to increase.
In particular, this phenomenon becomes conspicuous when performing scanning exposure at a low speed. In an actual process, since limitations are imposed by the resist sensitivity and the exposure image quality is of a primary importance, scanning exposure at a low speed is unavoidable. An exposure apparatus in which the scanning speed is variable to control the exposure amount is proposed in, e.g., Japanese Patent Laid-Open No. 9-106939. In this case as well, scanning exposure at a low speed may be performed.
When performing scanning exposure, respective stages in a conventional scanning exposure apparatus operate in the following manner.
{circle around (1)} The stages are accelerated up to a scanning speed determined by the process conditions.
{circle around (2)} The reticle stage and the wafer stage are synchronized, and transient response is controlled until the error (synchronization error) between them becomes a predetermined value or less. During this control operation, the stages idle. The period from when the stages reach a predetermined speed to the point, in time, when the synchronization error is equal to or less than a predetermined value and the exposure apparatus starts exposure, is called the settling time.
{circle around (3)} Light emitted by the light source is projected onto the wafer for an exposure field.
{circle around (4)} The stages are positioned in the same manner as in the control operation of the transient response performed in item {circle around (2)}. More specifically, the stages idle in the same manner as in item {circle around (2)} by a distance corresponding to the idling distance in item {circle around (2)}. Note that light projected onto the wafer in the next exposure field is scanned in a direction opposite to that for the immediately preceding exposure field. This is because to eliminate overlapping stage movement is advantageous in terms of throughput.
{circle around (5)} The stages are decelerated for the next shot until the speed becomes zero.
Items {circle around (1)}, {circle around (3)}, and {circle around (5)} are indispensable to satisfy the maximum acceleration limit for the stages and to assure the exposure field length. Regarding items {circle around (2)} and {circle around (4)}, they are usually determined by the maximum scanning speed possible for the apparatus, which is the strictest condition for the apparatus. Generally, the larger the scanning speed and the stage acceleration, the longer the settling time must be. FIG. 4 shows a stage deviation (synchronization error) waveform obtained by changing the scanning speed. When the scanning speed increases, the overshoot amount of the synchronization error increases, and the settling time is prolonged.
In the scanning exposure apparatus, the stroke amount of scanning of each stage must be determined by considering these conditions. In order to realize this, conventionally, the stroke amount was obtained by a process shown in the block diagram of FIG. 5. This determination process will be described.
A scanning speed setting unit 1 sets a scanning speed V under various conditions of the device manufacturing process. A stage acceleration/deceleration parameter setting unit 2 determines stage acceleration/deceleration parameters depending on factors such as the maximum acceleration possible for the stage. For example, when a stage acceleration/deceleration target position is to be generated in accordance with an S-shaped speed pattern, a maximum acceleration A and a time Tj required until reaching the maximum acceleration A are generated as the parameters. A settling time determination unit 22 sets a minimum value Ts allowed with the maximum scanning speed, as described above. An exposure field length (Xe) setting unit 4 is also provided.
Under these conditions, a stroke amount determination unit 5xe2x80x2 obtains a scanning speed reach stroke and a stroke necessary for deceleration from the scanning speed (corresponding to {circle around (1)} described above), a distance through which the stage travels within the settling time (corresponding to {circle around (2)} and {circle around (4)} described above), and an exposure field length (corresponding to {circle around (3)} described above), and calculates a stage stroke amount X as the sum.
As described above, in the prior art, the various types of parameters required when determining the stroke amount are processed as independent parameters. As described above, as the settling time, a value that satisfies both the maximum scanning speed and the maximum acceleration is used. Accordingly, the lower the scanning speed, the longer the settling time, which is a paradox. As a result, the throughput is sacrificed in this case.
The settling time is also influenced by the jerk time, the shot position, the scanning direction, and the like. In the prior art, the settling time is determined for the maximum scanning speed and the maximum acceleration that can be satisfied even under conditions or in occasions where the jerk time, the shot position, the scanning direction, and the like are the worst.
The present invention has been made in consideration of the problems of the prior art described above, and has as its object to provide an exposure method and exposure apparatus for increasing the throughput of scanning exposure. It is another object of the present invention to provide a method of manufacturing a semiconductor device by using such exposure method and exposure apparatus. The exposure method and exposure apparatus according to the present invention that achieve these objects have the following steps and arrangement, respectively.
That is, there is provided an exposure method of scanning and exposing a substrate at a constant speed, comprising variably setting, in accordance with a predetermined condition, a settling time which lapses from a time when a substrate reaches a constant scanning speed by acceleration to a start of exposure.
There is also provided an exposure method of scanning and exposing a substrate at a constant speed, comprising the steps of setting the constant scanning speed, and setting a settling time, which lapses from a time when a substrate reaches a scanning speed by acceleration to a start of exposure, variably in accordance with at least one of the scanning speed, an acceleration, a jerk time, and a shot position.
There is also provided an exposure apparatus for scanning a reticle and a wafer in synchronism to optically transfer a pattern drawn on the reticle onto the wafer, thereby forming a device, comprising first and second drive means for holding and scanning the reticle and the wafer, wherein the first and second drive means have a scanning distance which is determined by a sum of a first distance through which the drive means travel until reaching a scanning speed, a second distance through which the drive means travel during exposure, and a third distance through which the drive means travel during a settling time from a time when the drive means reach the scanning speed to a time when exposure is enabled, and the settling time is variably set in accordance with an exposure parameter.
There is also provided a device manufacturing method comprising the steps of setting a settling time, after which exposure can be started, under a predetermined condition by applying the exposure method described above, and exposing a wafer on the basis of the preset settling time to manufacture a device, wherein the settling time allows manufacturing the device with a maximum throughput.
There is also provided a device manufacturing method comprising the steps of preparing the exposure apparatus described above, and manufacturing a device with the prepared exposure apparatus.
According to a preferable aspect of the present invention, in the exposure method described above, the predetermined condition includes at least one of a scanning speed, an acceleration, a jerk time, a shot position, and a scanning direction of the substrate.
According to another preferable aspect of the present invention, in the exposure method described above, a sum of a distance required for acceleration, a distance required for settling, and a distance through which the substrate moves during exposure changes in accordance with the scanning speed.
According to still another preferable aspect of the present invention, in the exposure method described above, the settling time is set by using a function or look-up table in which a relationship between the settling time and the scanning speed tends to increase substantially monotonically.
According to still another preferable aspect of the present invention, in the exposure method described above, the function or look-up table is updated when necessary by using a result obtained by driving the substrate.
According to still another preferable aspect of the present invention, in the exposure method described above, the substrate is a reticle and/or a wafer employed when scanning a reticle stage and a wafer stage in synchronism to transfer a pattern drawn on a reticle onto a wafer by exposure.
According to still another preferable aspect of the present invention, in the exposure method described above, the settling time is set for only one of a reticle stage and a wafer stage which has a longer settling time.
According to still another preferable aspect of the present invention, in the exposure method described above, the settling time is set for only a wafer stage.
According to still another preferable aspect of the present invention, in the exposure apparatus described above, the exposure parameter is at least one of a traveling speed, an acceleration, a jerk time, a shot position, and a traveling direction of the substrate.
According to still another preferable aspect of the present invention, in the exposure apparatus described above, the settling time is determined by using a function or look-up table in which a relationship between the settling time and the scanning speed tends to increase substantially monotonically.
According to still another preferable aspect of the present invention, in the exposure apparatus described above, the function or look-up table is updated when necessary by using a result obtained by driving the drive means.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.